Effect of Doping Ti4+ on the Structure and Performances of Li3V2(PO4)3

Lithium-ion battery cathode material Li3.2x(V1.xTix)2(PO4)3 was synthesized using sol-gel/carbothermal reduction method. Electrochemical properties of substituted samples were investigated, which showed the enhancement of discharge capacity and the cycle performance by the substitution of Ti4+. The pure material of Li3V2(PO4)3 presented three plateaus around 3.58, 3.67, and 4.08 V, but the first two plateaus presented slightly sloping in the substituted samples and the boundary gradually became ambiguous with the increase in the substitution ratio. The differential thermal analysis (DTA) indicated that a stabilized γ-phase product was obtained. The crystal structure was characterized by the X-ray diffraction and the Rietveld method. The results showed that all the lithium sites were partially occupied, which introduced additional vacancies into the lithium sites. The ionic conductivity of doped material was increased to three orders of magnitudes. The disorder of lithium ion would correspond to the enhancement of the conductivity and specific capacity.